There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

BACKGROUND With a rising global population, increasing energy demands, and impending climate change, major concerns have been raised over the security of our energy future. Developing sustainable, fossil-free pathways to produce fuels and chemicals of global importance could play a major role in reducing carbon dioxide emissions while providing the feedstocks needed to make the products we use on a daily basis. One prospective goal is to develop electrochemical conversion processes that can convert molecules in the atmosphere (e.g., water, carbon dioxide, and nitrogen) into higher-value products (e.g., hydrogen, hydrocarbons, oxygenates, and ammonia) by coupling to renewable energy. Electrocatalysts play a key role in these energy conversion technologies because they increase the rate, efficiency, and selectivity of the chemical transformations involved. Today’s electrocatalysts, however, are inadequate. The grand challenge is to develop advanced electrocatalysts with the enhanced performance needed to enable widespread penetration of clean energy technologies. ADVANCES Over the past decade, substantial progress has been made in understanding several key electrochemical transformations, particularly those that involve water, hydrogen, and oxygen. The combination of theoretical and experimental studies working in concert has proven to be a successful strategy in this respect, yielding a framework to understand catalytic trends that can ultimately provide rational guidance toward the development of improved catalysts. Catalyst design strategies that aim to increase the number of active sites and/or increase the intrinsic activity of each active site have been successfully developed. The field of hydrogen evolution, for example, has seen important breakthroughs over the years in the development of highly active non–precious metal catalysts in acid. Notable advancements have also been made in the design of oxygen reduction and evolution catalysts, although there remains substantial room for improvement. The combination of theory and experiment elucidates the remaining challenges in developing further improved catalysts, often involving scaling relations among reactive intermediates. This understanding serves as an initial platform to design strategies to circumvent technical obstacles, opening up opportunities and approaches to develop higher-performance electrocatalysts for a wide range of reactions. OUTLOOK A systematic framework of combining theory and experiment in electrocatalysis helps to uncover broader governing principles that can be used to understand a wide variety of electrochemical transformations. These principles can be applied to other emerging and promising clean energy reactions, including hydrogen peroxide production, carbon dioxide reduction, and nitrogen reduction, among others. Although current paradigms for catalyst development have been helpful to date, a number of challenges need to be successfully addressed in order to achieve major breakthroughs. One important frontier, for example, is the development of both experimental and computational methods that can rapidly elucidate reaction mechanisms on broad classes of materials and in a wide range of operating conditions (e.g., pH, solvent, electrolyte). Such efforts would build on current frameworks for understanding catalysis to provide the deeper insights needed to fine-tune catalyst properties in an optimal manner. The long-term goal is to continue improving the activity and selectivity of these catalysts in order to realize the prospects of using renewable energy to provide the fuels and chemicals that we need for a sustainable energy future.

/pdf/combining-theory-and-experiment-in-electrocatalysis-insights-3l4yblici7.pdf

Combining theory and experiment in electrocatalysis: Insights into materials design

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron-hole diffusion lengths (typically about 10 nanometers). Recent reports of highly efficient CH3NH3PbI3-based solar cells in a broad range of configurations raise a compelling case for understanding the fundamental photophysical mechanisms in these materials. By applying femtosecond transient optical spectroscopy to bilayers that interface this perovskite with either selective-electron or selective-hole extraction materials, we have uncovered concrete evidence of balanced long-range electron-hole diffusion lengths of at least 100 nanometers in solution-processed CH3NH3PbI3. The high photoconversion efficiencies of these systems stem from the comparable optical absorption length and charge-carrier diffusion lengths, transcending the traditional constraints of solution-processed semiconductors.

https://dr.ntu.edu.sg/bitstream/10220/16761/1/long-range balanced electron- and hole-transport lengths in organic-inorganic ch3nh3pbi3.pdf

Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3

Controlling the morphology of nanomaterials is important for their fundamental study and practical application. Especially one-dimensional nanowires, nanorods, and nanotubes and two-dimensional nanoplates possess interesting physical and chemical properties due to their structural anisotropy. The key to obtaining these morphologies is to break the symmetry of crystal growth to promote anisotropic growth. In this chapter we discuss the catalyst- and template-free screw-dislocation-driven nanomaterial growth mechanism, in which an axial screw dislocation creates self-perpetuating growth steps upon intersecting with the crystal surface and enables anisotropic crystal growth under low supersaturation conditions. The presence of screw dislocations not only alters the growth kinetics of nanomaterials, but also distorts the crystal lattice and generates a strain field, both of which lead to morphology variation of the nanomaterials. The structural characteristics associated with dislocation-driven growth can be readily detected using transmission electron microscopy techniques. A review is presented on a wide range of nanomaterials formed under various conditions whose growth has been confirmed to be driven by screw dislocations, demonstrating the generality of this mechanism. A framework for rationally synthesizing anisotropic nanomaterials via dislocation-driven growth is provided. This will enable large-scale, low-cost production of nanomaterials for various applications.

Growth of Nanomaterials by Screw Dislocation


 The concept of topology has dramatically expanded the landscape of magnetism, leading to the discovery of numerous magnetic textures with intriguing topological properties. A magnetic skyrmion is an emergent topological magnetic texture with a string-like structure in three dimensions and a disk-like structure in one and two dimensions. Skyrmions in zero dimensions have remained elusive owing to challenges from many competing orders. Herein, by integrating electron holography and micromagnetic simulations, we uncover the real-space magnetic configurations of a novel skyrmionic vortex structure confined in a B20-type FeGe tetrahedral nanoparticle. This texture shows excellent robustness against temperature without applying a magnetic field; an isolated skyrmionic vortex forms at the ground state. These findings shed light on zero-dimensional geometrical confinement as a route to engineer and manipulate individual skyrmionic metastructures.

/pdf/geometrically-stabilized-skyrmionic-vortex-in-fege-2490ulee4c.pdf

Geometrically Stabilized Skyrmionic Vortex in FeGe Tetrahedral Nanoparticles

Monotopic binding modes for ditopic ligands: synthesis and characterization of W6S8L6 (L = bis(diphenylphosphino)ethane, 4,4′-bipyridine) cluster compounds

We develop rational chemical strategies to synthesize novel one-dimensional nanowire materials of transition metal silicides, investigate their physical properties, and use them as nanoscale building blocks for the bottom-up assembly of integrated photonic, electronic, and spintronic nanosystems. Transition metal silicides are extremely important to microelectronics because of the ohmic contact and interconnect many silicides (NiSi, CoSi 2 , and TiSi 2 ) provide. Furthermore, many silicides are direct bandgap semiconductors (CrSi 2 , β-FeSi 2 ) and are promising for silicon-based photonics. The recent discovery of Fe x Co 1-x Si alloys as ferromagnetic semiconductors make them promising for spintronic applications as well. Herein, we describe the chemical synthesis of free standing single-crystal nanowires (NWs) of FeSi, the only transition metal Kondo insulator and isostructural CoSi, an important metallic silicide for CMOS electronics. Straight and smooth FeSi and CoSi nanowires are produced on silicon substrates covered with a thin layer of silicon oxide through the decomposition of the single source organometallic precursors trans -Fe(SiCl 3 ) 2 (CO) 4 and Co(SiCl 3 )(CO) 4 , respectively, in a simple chemical vapor deposition (CVD) process. Unlike typical vapor-liquid-solid (VLS) NW growth, silicide NWs form without the addition of metal catalysts, have no catalyst tips, and depend strongly on the surface employed. The physical properties of these new FeSi and CoSi nanowires, including electrical transport and X-ray spectroscopy, are reported. This general approach to silicide nanowire growth is likely to yield other functional silicide nanosystems with significant applications in nanoelectronics and nanophotonics, and for Fe x Co 1-x Si, silicon based spintronics.

Synthesis, characterization, and physical properties of transition metal silicide nanowires

Reductive immobilization has been a commonly used technique to detoxify Cr(VI) from soil; however, it's challenging to remove the reduced Cr from soil to prevent its re-oxidation. This work explored a natural magnetic composite for the remediation, mineralization, and magnetic removal of Cr(VI) from the soil. It consists of 77% magnetite and 23% pyrrhotite with strong magnetic properties. A series of characterization tests show that composites of magnetite and pyrrhotite are interlaced and closely bonded, and contain no other heavy metals. The Cr(VI) removal rate increases with the decrease in composite particle size. A kinetics study shows that removing Cr(VI) by the composite is likely through both adsorption and reduction. Acidic conditions are more favorable for the immobilization of Cr(VI), at 45.8 mg Cr(VI) removal per g of composite at pH 2. After 100 days of in-situ treatment by the composite, the leaching concentration (TCLP) of Cr(VI)-contaminated soil was 1.95 mg L-1, which was below the EPA limit (5 mg L-1) for hazardous waste. After reduction, the composite was separated from soil by magnetic characteristics, and 58.2% of Cr was found mineralized. The post-treatment Cr-containing composite was analyzed by SEM-EDS, Raman spectra, and XPS. It was found that Cr was mineralized on the surface of the composite in the form of Cr(OH)3, Cr2O3, and FeCr2O4. This indicates that reduction and mineralization of Cr(VI) in the soil can be accomplished through natural magnetic mineral composites and easily separated and removed from the soil, achieving a complete soil cleanup. 

https://doi.org/10.1016/j.ese.2022.100181

Song Jin

Papers

Growth of Nanomaterials by Screw Dislocation

Geometrically Stabilized Skyrmionic Vortex in FeGe Tetrahedral Nanoparticles

Monotopic binding modes for ditopic ligands: synthesis and characterization of W6S8L6 (L = bis(diphenylphosphino)ethane, 4,4′-bipyridine) cluster compounds

Synthesis, characterization, and physical properties of transition metal silicide nanowires

Reduction, mineralization, and magnetic removal of chromium from soil by using a natural mineral composite